#include <iostream>
#include <fstream>
#include<cmath>
#define dim 2000005
using namespace std;


ifstream in("ciur.in");
ofstream out("ciur.out");
bool c[2000000];
int main()
{
    int n,nr=0;
    in >> n;
    for (int i = 2; i <= sqrt(n); i++) 
    {
        if (c[i] == 0) 
        {
            for (int j = i * i; j <= n; j += i)
                c[j] = 1;
        }
    }
    
    for (int i = 2; i <= n; i++)
        if (c[i] == 0)
            nr++;
    out << nr;



   return 0;
}